Vulcanization of rubber



Patented May 19, 1942 a v VULCANIZATION or RUBBER Arthur M. Neal, Wilmington, DeL, and Bernard M. Sturgis, Pitman, N. J., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application July 18, 1940,

' Serial No. 346,140

23 Claims.

This invention relates to'the vulcanization of rubber and more particularly to new combinations of accelerators for the vulcanization of rubber.

It has been proposed to accelerate the vulcanization of rubber with a combination of accelerators ofwhich oneisdesignated the primary accelerator and the other is designated a secondary accelerator. The purpose of the secondary accelerator is generally to activate the primary accelerator with an acidic primary accelerator,-

such as the mercapto-thiazoles and particularly Z-mercapto-benzothiazdle, because of the great activity of such combinations of accelerators. Generally, such combinations of dithiocarbamates and mercapto-thiazoles render the rubber incapable of being processed due to its tendency to pre-vulcanize or scorch. Furthermore, combinations of dithiocarbamates with mercapto-thiazoles andother similaracidic accelerators have been found to impart inferior physical properties to the'rubber. The resulting vulcanizates are generally poor in resistance to abrasion and in resistance to aging. Further, such combinations of accelerators usually cause bad reversion of the rubber at the longer cures, which is accompanied by a loss in tensile strength and a deterioration of the physical properties in general.

It is an object of the present invention to provide-an improved method of vulcanizing rubber. Another object is to provide vulcanized rubber of improved properties. A further objectis to improve the vulcanization of rubber by employing,

- as acceleratorstherein, new combinations of accelerators which are sufficiently safe at processing temperatures for commercial utilization and which are at the same time very active at normal vulcanization temperatures. A still further object is to provide a new combination of accelerators for the vulcanization of rubber which produces vulcanized rubber of improved properties. Other objects are to provide new compositions of matter and to advance the art. Still other objects will appear hereinafter.

The above and other objects may be accom plished in accordance with our invention, which comprises employing, as accelerators for the vulcanization of rubber, a 2-mercapto-thiazoline accelerator, as a primary accelerator, and a dithiocarbamate accelerator, as a secondary accelerator. We have found that, when such accelerators are employed together for accelerating the vulcanization of rubber, novel results are obtained, which are different than would be expected from the results which have been obtained when it has been attempted to employ the dithiocarbamates with mercapto-thiazoles, such as 2- mercapto-benzothiazole, and similar acidic type accelerators. We have. found that the 2-mercapto-thiazoline accelerators can be activated with dithiocarbamate accelerators so that stocks will be obtained, which can be processed safely but which will produce vulcanizates possessing exceptionally good moduli and tensile properties I ber, vulcanized by the jointemployment of the.

accelerators of our invention, has very-good' resistance to deterioration. In particular, it is re- V abrasion, excellent resistance to flex-cracking and excellent resistance to tear, both at ordinary atmospheric temperatures and at higher temperatures.

The tensiles, determined at 100 C., are

wherein X represents an organic group or a salt forming group or element, It represents hydrogen or an organic radical and R1 represents an. organic radical. While either or both of R and R1 may represent aromatic radicals, preferably, at least one of R and R1 represents an aliphatic and, particularly, an alkyl radical. We particularly prefer that R and R1 each represents an aliphatic and, specifically, an alkyl radical. In some cases, it will be preferred that R and R1 together represent a saturated carbon chain having the terminal carbon atoms of the chain directly bonded to the nitrogen to form a heterocyclic ring such as pentamethylene and hexamethylene. The dithiocarbamate accelerators, which may be employed in accordance with our invention, will include amine salts, metal salts, carbamyl and other acyl derivatives, esters and sulfides of the various dithiocarbamic acids. The

sulfides. oi the dithiocarbamic acids will be designated hereinafter by the more commonly employed names, as thiuram sulfides.

By the term alkyl, as employed hereinafter and in the claims, we mean an aliphatic radical which consists of carbon and hydrogen and which contains no aromatic rings. By the term aliphatic, we means that the radical may contain aromatic, as well as non-hydrocarbon substituents. I

In order to illustrate the remarkable propaccording to our invention, results of tests, in which combinations of various dithiocarbamates with 2-mercapto-thiazolines have been used, are here described.

A particularly valuable class of activators for 2-mercapto-thiazolines consists of carbamyl derivatives of dithlocarbamic acids. In order to show the extreme safety of these combinations at processing temperatures together with the very desirable properties obtainable at vulcanizing temperatures, the following stocks were prepared.

erties that can be obtained when rubber is treated Stock C, in which Z-mercapto-benzothiazole is used as the primar accelerator, was run for purposes of comparison with corresponding stock Bin which 2-mercapto-thiazoline is used as the primary accelerator. The results, of the vulcanization tests on these stocks, are given in Table I.

TABLE I Modulus at 500% elonga- Tensile at break (lbs./ Min Temgation (lbs/sq. in.) sq. in.)

petacured tum Stock A Stock B Stock 0 Stock A Stock B Stock 0 No cure 225 225 150 1, 700 550 300 These results show that, when phenyl methyl carbamyl dimethyl dithiocarbamate is used as a secondary accelerator with 2-mercapto-thiazoline, a powerful activating effect is obtained at 274 F. The modulus of the stock is tremendously increased, being almost doubled in the shorter cures. The tensiles also are raised considerably on the shorter cures. obtained with a very high modulus, and a flat curing curve showing no reversion. However,

this activation is not obtained at the expense of processing safety, for the activated stock is even safer at processing temperatures than the one containing unactivated 2-mercapto-thiazoline.

This stock is an idealone for the preparation of many types of rubber articles. Stock C, in which z-mercapto-benzothiazole was used as the primary accelerator, does not show the high moduli or tensiles of stock B. Furthermore, bad reversion is apparent with stock 0, as the modulus and tensile figures fall off markedly. This stock 0 is entirely undesirable.

In order to show that the results, obtained above, are not limited to the particular test formula used, the following stocks were prepared.

Thus a stock is carbamyl dithiocarbamates are powerful activa- 30 4 Stock tors for 2-mercapto-thiazolines, the modulus,

after 20 minutes of cure, being approximately M o P goubled. Thtese combinations of accelerators are, g l l fig fi g 2g 2g gg m m0 owever, ex ren'lely safe, giving no cure after 35 zincoxlde 6 5 5 5 45 minutes at 227 F. Carbamyl dlthiocar- 3: acid. g g g g I uf bamates function equally well with carbon sub- 2-mercapto-thiazoline-- 0.5 0.5 0.5 0.5 0.5

ocar ma 3 of 2 mercapto thiazolines, as shown by the re Hexamthylenmmmm sults of tests on stocks H, I, J, and K. These nium-hexamethylene dlthiocarbamate 0.05 combinations, of caroamyl dithiocarbamates with ni-laur ylu i i monium-di- 0 I 2-mBrcapto-thiazolines, therefore represent the Burp ocarbamate" Ideal condmon of glvmg fast hlgh modulus The result of these tests, which were carried G, in which 2-mercapto-bnzothiazole was TABLE 111 used as the primary accelerator, clearly show that this compound does not give a satisfactory cure M e p- St ck St ck t c St Stock 50 cured cured L M N 0 P when used in con unct1on with a carbamyl dithioarbama If b my m ate is used MODULUS AT 500% ELONGATION, Les so. IN. with Z-mercapto-benzothiazole, in an amount 5 0 F sufficient to give any substantial amount of ac? 55 30 227 225 350 No cute 25 75 tiva'tion, the resulting rubber is so badly over- 45 a 227 325 750 425 1e 274 1,375 2,325 2500 575 1,075 cured as to be worth 8 274 2, 550 3,475 31375 925 1,525 Another class of dithiocarbamate derivatives, 274 3, 3,375 3,325 1,275 1,975 274 3, 350 4, 1 3, 975 1, 450 2, 175

- 2,288,834 3 The results, 01 thevulcanization tests on these gum stocks, are givenin Table II. I

TABLE II V OF I 30 227 No cure N o cure No cure I. 75 75 75 45 227 150 No cure No cure 1 20 274 1,300 2,500 2,500 2,450 '075 1,525 550 1,250 4 30 274 1,500 3,325 2,950 (r '875 1,700 050 1,475 45 274 2, 225 3, 350 2, 225 2' 00 274 2,550 3,475 2,775 1, 325 2,075 1,025 1,500

TENSILE 4'1 BREAK, LllSJSQ. IN.

227 No cure No cure No cure 300 300 250 350 227 500 Nocurc Nocure 274 3,200 4,425 4,775 2,450 2,550 3,825 2,275 3,375

Broke short.

These results show that, in a gum stock also,

flat curin curve type' o cure, co p ed wi 45 out in both a gum stock and a black stock, are fect processing safety. The tests on stock given in Table III.

that produces excellent results when used as secondary accelerators with 2-mercapto-thia75oles, TENSILE AT BREAK, LBSJSQ. IN. consists of substituted ammonium salts of dithio- 30 227 475 525 No cure 475 375 carbamic acidstoTms clatss 150f 60111301121415 l'as 45 227 525 1,025 825 1,350 2,160

n 1 a ors r not been usfad any ex a v o 20 274 2,925 4,225 3,550 2.025 3.400 mercapto-thiazoles and other s1m1lar acidic ac- 30 274 3,525 4,950 4,475 3,250 3,975 45 274 4,425 5,075 4,300 3,725 3,800 celerators smce the resulting combinations are 60 274 4,350 4,825 4,450 3,350 3,825 too active at processing temperatures for use. 2- mercapto-thiazolines, on the other hand, can be 1 By comparing stocks L, M, and N, it can beactivated with safety with ammonium salts of Seen thahif a Small mount of a substituted ammonium salt of'a dithiocarbamic acid is added dithiocarbamates.

to stock L, the modulus and tens11e figures, at

, In orger to W the Y i of our mven' curing temperatures, are considerably increased. tion, the following s c w compounded and Even though this class of compounds is consid-' cured, v ered among the most active as rubber accelerators, yet its members can be used with safety in combination with a 2-mercapto-thiazoline,

- the resulting stocks (M and N) showing no tendency to prevulcanize during processing. It can also be noted that no reversion in the modulus is present at 274 F., but rather the modulus steadily increases throughout the cure. The same efiects are noted in stocks and P, in which a gum type formula was used.

Another extremely active class of rubber accelerators are the metal salts of dithiocarbamic acids. The activity of these compounds is so great that they can seldom be used with mer- Stock L Q R O S T U Smoked sheets 100 100 100 100 100 100 100 25 25 25 5 5 5 5 5 5 3 3 3 3 3 8 3 Sulfur 3 3 3 3 3 3 3 2-mercapto-thiazoline. 0.5 0.5 0.5 0.5 0.5 0.5 05 Zinc hexamethylene dithiocarbamate. 0.05 0.1 0.05 0.1 Lead-dibutyl-dithio- 1 carbarnate 0.1

In these tests, both gum stocks and stocks containing carbon black, were used. Also, the amount of secondary accelerator has been varied to show that it can be widely varied. The amount 0 of secondary accelerator may be reduced much below the lowest amount here used and still retain its activating efiect. Results of these tests are given in Table IV.

used as rubber accelerators, consists of the thiuram sulfides. These also produce very desirable rubber vulcanizates when used in combination with a Z-mercapto-thiazollne. This is il- 5 iustrated by the following test made on a rubber compound of the composition:

. Stock V I Smoked sheets 100 Zinc oxide 5 Channel black 25 Stearid acid 3 Sulfur. 3 2 mercapto 011152011115 0.92 Tetramethyl thiuram mono sulfide--- 0.03

This stock was cured for 30, 45, 60, and 90 minutes at 274 F. and the following test data were obtained.

' TABLE V Modulus- Minutes Tensile cure de gggggfi at break, 274 F. lbsJsqdm lbs/sq. in.

There was no difiiculty in processing this stock, but, as shown in the table, when it was cured at 274 F., rubber having very high moduli and tensile strength was obtained.

Tetramethyl thiuram disulflde and dipentamethylene thiuram tetrasulfide were used as activators for Z-mercapto-thiazoline in the followingrubber stocks:

Stock Stock Stock A1 B5 1 100 100 100 5 5 5 2 2 2 1 1 1 3 3 3 Z-mercapto-thiezoline 1 0. 76 0. 75 Tetramethyi thiumm disuiflde 0. 025 Dipentamethylene thiuram tetrasulflde 0.025

TABLE IV {333- Stock L Stock Q BtoekR Stock 0 Stocks Stock! StcekU MODULUS AT 500% ELONGATION, LBSJSQ. IN.

2 F. I 20 227 No cure No cure No cure No cure 175 No cure 2 221 225 Nocure 450 '25 125 015 25 20 214 1,015 2,215 2,015 01 1,525, 2,025 1,500 20 214, 2,550 2,125 2,125 025 2,115 2,015 2,100 45 214 2,015 2,550 4,215 1,215 2,215- 2,050 2,215 50 214 2,250- 4,100 1,450 2,500 2,015 2,415

TENBILE ,4'1 BREAK, LBS./SQ.1N.

20 '227 NocureNccure 55011555511555" .500 Nocnre 20 221 415 No cure 125 415 1,215 1,025 20 214 2,025 2,425 4,000 2,025 2,005 4,525 2,115 20 214 2,525 4,415 5,025 2,250 2,550 4,200 2,025 45 214 4,425 4,225 4,015 2,125 4,015 2,015 4,025 00 214. 4,050 4,515 4,225 2,050 2,425 2,000 2,515

Here again, very high modulus stocks are ob- These stocks were vulcanized at 259 F, for

tamed without accompanying reversion or loss of processing-safety.

Another class of chemical compounds, widely periods of 30, 60 and minutes. The results, of modulus andtensile tests on the stocks after vulcanization, are given in the following table:

' stocks were prepared:.

' TA'sLsIVT a 1 Table VIII gives the results of the tests on y i compounds. '1 a 4 StockA StoakB StockC I a l TABLEVIII v Min. Temp. cured cured 600% 7 Big)? 600 a 5 modu- Tensile m u- Tensile me u- Tensile Modulus 0 93 1 Tensile at break,

1118 1' 1118 gation, lbs./sq. in. lbs/sq. in. Min. "1 1 F cured C St 2' Stock Stock' Stock St k Etek so 259' v 515 3,100 1,15o' 3,915 v1,050 4,150 .f w x L 227 No No No No No No It can be seen from these results 1hat both of these thi'urams are powerful activators for 2- mercapto-thiazoline, only a very small amount being necessary to double the modulus and greatly increase the .tensile on the 30 minute cure. Moreover, these activators do not cause overcuring or reversion when used in these amounts, since the modulus has not started to fall off even veases es s after 120 minutes of cure, Furtherm r no 111. o The combinations of accelerators, used in these flculty was encountered in processing any {of tests, can be seen to 'give excellent cures at ordithese stocks; r J nary vurcanizing temperatures, but to retain In order to illustrate that metal salts of 2- good p sin 's fe ymercapto-thiazolines can also-be efiectively acti- A large number f esters. of fl j c,

vated with the thiuram sulfides, the following acids have been disclosed in patents and in the literature. Many types of these esters are valuable as activators for 2-mercapto-thiazolines. In stock stock E1 order to illustrate their usefulness, the following 1 stocks were prepared. Smoked sheets -1 100 100 Zine Mills 5 6 Channelblack"; 25 25 Stock Btearic acid 3 3 Sulfur 3 3 Zinc salt of 2-mercapto-thiezoline 1 0.97 O Y Z Tetramethyl thiuran monosuliidea 0.03 Y 1 Results, of tests on these stocks, are given in 2 Table'VII. A .g

. lflfur 3 1 TABLEVH 2-111 mgpto-th1 mm 0.5 0.5 0-5 v A I 2,4-dinitrophenyl-hexamethylene, dithio I StOOk l, StockE i' gg d M t 0.25 4 1m r 3532a E methgl-dit ii cstbama euitfiiri "I..." 0.25 l ured 600.7 I I 60W 7 4 I Modufus Tensile Mod us P e I Results, of tests on these stocks, are given in Table DI. 4 r I 20 227 Nocure Nooure Nocure News 4 30 227 '25 126 No cure Nooure TABLE Ix 7 so 221- 125 1,115 450 1,100 1 Modulus 51500 1, elon- Tensile at break, lbs./

20 214 850 015 550 1 525 j 214 km gm @115 .2525 Ma i I 45 214 3,125 4,415 3,525 I 4,9505 Cured 1 g. 3%? 2% {3 g Stock Btook' Stock stock Stock Stgck w 2" '0" e A Y z Y It can be. seen thatfthe-addltion of a small v a 4 amount of a thiuram sulfide gives a substanm 9 ti'al increasein the-modulus and tensile figures W4 675 1,750 2Rm0 4175 .at 27.4 1".- without givingany decrease in safety i}? 313% 2% "21% 21312 i at-processing temperatures. 1 274 L M 2,500 3,859

licyl derivatives oi.- dithiocarbamic acids, which: 7 j may conveniently be-prepared by reactingan acid It .can be seen that it is possible. to obtain -chloride with a-metalsalt of a dithiocarbamic vuleanizates having very desirable properties the following comp unds;

acid.j also providesa've'ryl desirable class of-sec through the use of combinations of dithiocar- I endaryaccelerators'for use with 2-mercaptobamates with 2-'mercapto-thiazolines. Such vulthiazolines. The desirability of thes'e combina-y. canizates may be processed with safety as istions is illustrated by the results of tests made on shown by thetests made on the 227 F. cures.

' The-extreme safety of these'combinations permitsa wide latitude invthe selection of the acceleratorlcombinations and inthe, amounts of both the primary and secondary accelerators usedin the eombinatioi1s. v- 1 i .Not only do the .vulcanizates, prepared accordj ing toour invention', possess-excellentmodulus and tensile properties, freedom .rrom reversion, and ,proeessing safety,- but they .are 1 also" characterized by manyother-'y-valuable properties which" make them desirable commercial 'v-ul- One property of vulcanized rubber, which is very important for many applications, such as the construction of inner tubes for tires, is its resistance toward tearing. Vulcanizates, prepared according to our invention, have very excellent tear resistance, as shown in Table X. This excellent tear resistance cannot be obtained by combinations of dithiocarbamates with. mercapto-thiazoles, since an overcured condition generally results which causes a deterioration of physical properties. Tests were made, using gum stock and carbon black stock L as the basic stocks. Stock AA is stock 0 .with the addition of 0.15 part of phenyl-ethyl-carbamyl-pentamethylene-dithiocarbamate; stock BB is stock 0 with the addition of 0.04 part of hexamethyleneammonium hexamethylene dithiocarbamate; stock CC is stock 0 with the addition of 0.025 part of zinc-hexamethylene-dithiocarbamate. Likewise, stock DD is stock L with the addition of 0.15 part of phenyl-ethyl-carbamyl-pentamethylene-dithiocarbamate.

' TABLE X Tear test at 28 0.

Min. .Stock Stock Stock Stock Stock Stock curedat 0 AA 4 BB 00 L DD These tests show that, although the modulus is greatly increased by the addition of the secondary accelerator, the stocks are not overcured, since the tear test is equal or superior to that given by theprimary accelerator. alone.

The ability of rubber to stand'up under high temperatures, while in service, is becoming in- The rubber industry is therefore desirous of obtaining a rubber vulcreasingly more important.

canizate having high modulus and tensile. fi res which will also be resistant to conditions of high 4.5 thiocarbamate alone (stock EE), aged very-poorly in both types of-test. 2-mercapto-benzo-thiatemperature without deterioration.v The combinations 'ofac'celerators of this invention will provide these desired characteristics. This is "illustrated by the test results given in Table XI, in which the results of tensile strength determi- Y nations made at 100 C. on stocks AA, BB, CC and 50 DD, are presented.

I TABLE XI It has been found, however, that, when these dithiocarbamates are used as activators for 2- mereaptothiazolines inaccordance with our invention, this deterioration, in age and heat resistance, is not apparent. The resulting vulcanizates withstand deterioration to a remarkable degree. This is illustrated by the results given in Table XII. The tests, recorded inthis table,

were'carried out on the following stocks.

Stock EE FF GG BB 15 Smoked sheets 100 100 100 100 Zinc oxide 5 5 A 5 l0 Stearic acid 2 2 2 2 Sulfur 3 3 3 2.75 Phenyl-beta-naphthylamin 1 1 1 1 z-mercapto-thiazollne 0.75 0.75 2-mercapto-benzo-thiazole 0.85 2 Zine-hexamethylene-dithiocarbamate"--. 0.2 0.02

Hexamethglene ammonium hexamet ylene-dithiocarbamate 0.025

I These stocks were cured for minutes at 259 25, F. and then aged by suspending in an air oven at 100 C'.'for two days, and also'by suspending them in an oxygen bomb at 300 pounds oxygen pressure at C. for 14 days. In Table XIII,

there are given the original moduli at 500% elon-. 30 gation, tensiles at break, and also the tensiles 'after the completion of both aging tests.

Tum 1m Original 1 After 14 days 5 After 2 days in 70 0. Stock 5 W in loo (3 o ge 0V6 I18 8 m 11-" modul us Tensile sile The results of these tests are-rather surprising.

As was expected, the stock, containing the dizole, however, is noted as being one of the very few accelerators having antioxidantproperties. Dinsmore andVogt-TransfI, R. I. vol. 4, page 98. show clearly that 2-mercaipto-benzo-thiazole and para-nitroso-dimethylaniline are the on y Tensilesat break, lbs/ sq. tn,

Stock AA BtoclrBB Stock 00 Stock DD Min. cured e a at274F.

2s v as 100 2s 100 2a 100 a. "c. *0. c. 0. c. c. .0.. 3,925 3, 425 3, 475 2, 575 3, 325 3, 350 4,150 3, 250 4, 400 3, 000 3, 500 4, 050 3, 875 4, 675 3, 875. 4, 125 a, 350 a, 950 3,875 4, a, 925 4,925 ,900 3,825 -3, 275 3,800 3,575 3,900 3,225 4,825 3,800 3,825 3,325 3,675 3,175 3,175 2,325 4,125 3,775

' Rubber, vuieanizubythe use of dithiocarbamatesras accelerators, is notoriously poor-in age p and heatresistance- This poor resistance to-'v ward deterioration carries over-into 'stocks in which dithi'ocarbamates are. used 'as activators for mercapto-thiazeles and other similar types,

of accelerators. These combinations of accelerstars are therefore valueless for he preparation of most commercial two, oia large number ot commercial accelerators tested-which also acted as antioxidants Furthermore, Barron, in the book "Modern Rub -7o. ber Chemistry".'Hutchinson (1-937) onpage 194,

states that-z-mercapto-jbenzo-thiazole has a profound; retardingeflect on aging. These,

statements have been borne. out by observations in therubber industry that stocks, cured with 2- -mercabto-'-benzo-thiazole. havev very good agin sees characteristics. The addition of small amounts of a dithiocarbamate, however, greatly lowers the age resistance of the stock. On the other hand, it can be noted, from Table XII, that combinations of dithiocarbamates with" a 2-mercaptothiazoline produce vulcanizates that are greatly superior to those, prepared "from 2-merc ptoe benzo-thiazole, in resistance to aging in the 100 C. oven, and are somewhat superior inresistance to aging inthe oxygen bomb. It therefore appears that rubber vulcanizates, prepared according to our invention, are extremely valuable to the rubber industry since they resist deterioration better than the accelerator formerly adopted as the standard. 1

Besides the above described valuable properties of vulcanizates, prepared with'the accelerator these vulcanizates I combinations of our invention, also possess very good resistance to abrasion, flexcracking, and heat build-up. t

- Although certain definite combinations of accelerators have been shown, these combinations are illustrative rather' than limiting. A great many different Z-mercapto-thiazolines may be used as the primary accelerator with excellentresults. These include carbon substituted 2- mercapta-thiazolines in which one or both of the the 4 or or both the 4 and hydrogen atoms, in 5 positions of the ring, are substituted by alkyl groups or hydroxyalkyl groups as illustrated by the formula.

Q S l 3 Examples of I such substituted 2-mercapto.-' thia'zolines are: 4-ethy1-2-mercapto -thlazoline 4-propyl-2-mercapto-thiazoline 4,4-d1methyl-2mercapto-thiazoline 5,5-dimethyl-Z-mercapto-thiazoline 4-methyl-4-ethyl-2-mercapto-thlazoline 4,4-dimethyl-5-propyl-2 -'mercapto-thi azoline 4-isopropy1-5-propyl 2-mercapto-thiazoline 4-ethyl-5-propyl-2-mercapto-thlazoline 4-niethyl-5-hydroxymethyl-2-mercapto thiazo line .i 4-methyl-4 ethyl-E-propyl 2 mercapto-thiazo line 4-;ethyl-5-methyl-2 -mercapto-thiazoline 4-propyl-5-propyl-2-mercapto-thlazoline 4,5-dimethyl-2 -mercapto-thiazoline 4-hydroxyethyl-Z-mercapto-thlazoline 4,4,5,5-tetramethyl-2-mercapto-thiazoline Also, various metal salts of these .Z-mercaptothiazollnes may be used effectively. These include, among others,

Lead salt of 2-mercapto-thlazoline Calmium salt of 2'-mercapto-thiazoline Iron salt of Z-mercapto-thiazoline Zinc salt of 4-methyl-2-mercapto-thiazoline Cadmium salt of 4-methyl-21nercapto-thiazoline Zinc salt of 4ethyl-2-mercapto-thlazollne I Lead salt of 4-propyl-2-mercapto thlazoline Cadmium salt of 4,4-dimethyl-2-mercapto-thlazoline -Iron salt of 5, -dlmethyl-z-mercapto-thiazoline Zinc salt of l-methyl-4-ethyl-Z-mercaptmthiazoline Y Cadmium salt or 4,4-dimethyl-5-propyle2-mercapto-thiazollne v a line l Zinc salt of 4,4,5,5-tetramethyl-2-mercapto-thiazoline A large choice of members of the various classes of dithiocarbamic acid derivatives, employable as secondary accelerators, is also possible. For example, the following carbamyl dithiocarbamates are a few of the many that have been" found to be very efiective in producing the desired; re-

sults.

' Phenyl-methyl-carbamyl-diethyl-dithiccarbamate Phenyl-methyl-carbamyl-pentametnylenedithiocarbamate Phenyl-methyl-carbamyl-dicyclohexyl-dithiocarbamate 'Ethyl-cyclohexyl-ammonium-eth l-c Methyl-ethyl-ammonium-met Phenylethyl-carbamyl-diethyl-dithlocarbamate Phenyl-ethyl-carbamyl-dipropyl-dithlocarbamate Ihenyl-ethyl-carbamyl-dmmyl-dithioearbamate Phenyl-othyl-carbamyl-hexamethylene-dlthiocarbamate Phenyl-ethyl-cm'bamyl-dlcyclohexyl-dithiocarbamate Phenyl-ethyl-carbamyl-cyclohexyl-dithioearbamate Phenyl-ethyl-carbamyl-tetrahydtofuriuryl-dlthiocarbamnte Ethyl-o=to1yl-carbamyl-dimothyl-dithiocarbamate Ethyl-o-tolyl-carbamyl-pentamethylenadithiocarbamate Ethyl-alpha-naphthyl-carbamyl-dimethyl dithiocarbamate Ethyl-alpha-naphthyl-carbamyl-pentamethylene-dithiocarbamato Diphenyl-carbamyl-dimethyl-dithiocarbamate Diphenyl-carbamyl-hexamethylene-dlthiocarbamate Dimethyl-carbamyl-dimethyl-ditmocarbamate Dimethyl-carbamyl-pentamethylene-dithiocarbamate Phenyl-ethyl-carbamyl phenyl-ethyl-dithiocarbamate Diphenyl-carbamyl-phenyl-ethyl-dithiocarbamate Likewise, the substituted ammonium salts o dithiocarbamic acids disclosed in the examples, are only a few of the large number that have been tested-and which show very good results, Among these are- Di-benzyl-ammonium-di-benz Lauryl-ammonium-lauryl-dithiocarbamate Alpha-methyl-pentamethylene-ammonium-methyl-pentamethylenedithiocarbamate Ammonium-dibutyl-dithiocarbamate Butyl-pyridinium-dimethyl-dithocarbamate Tetramethyl-ammonium-dimethyl-dithxocarbamate enyl-guanidine salt of dimethyl-dithiocarbamic acid Diphenyl-guauidine salt of pentamethylene-dithiocatbamlc acid A large number of metal salts of dithlocarbamlc acids have been found to be effective secondary accelerators for 2-mercapto-thiazolines and their salts. Examples are the following- Zinc-dimethyl-dithioearbamate Oadmium-dimethyl-dithiocarbamete Lead-dimethyl-dithiocarbamate Ferrous-dlmethyl-dithiocarbamate Ferric-dimethyl-dlthioeatbamate Mercuriedimethyl-dithiocarbamate Aluminum-dimethyl-dithiocarbamate Stalmous-dimethyl-dlthiocatbamate Cobaltous-dimethyl-dithiocarbamate Nickelous-dimethyl-dlthiocarbamate Silver-dimethyl-dithiocarbamate Zino-pentamethylene-dlthloearbamate Cadminm-pentametbylene-dithiooarbamate Lead-pentamethylene-dithiocarbamate Ferrous-pentamethyleno-giithiocarbamate Ferric-pentamethyleno-dithiocarbamate .Aluminum-pentamethylene-dlthiocarbamate 0hromium-pentamethyleneaiithlocarbamate Stannous-pentamethylenerdithiocarbamate Cobaltous-penta.methylene-dithiomrbamate Nlckelous-pentamethylene-dithiocarbamato Silver-pentamethylene-dithlocarbsmate Cadmlum-hexamethylene-dithlocarbam ate Lead-hexamethylene-dithiocarbamate Fertous-hexamethylene-dithioearbamate Mercurlc-hexamothylene-ditbiowrbamate Zlnc-diethyl-dlthloearbamate V Cadmmm-dlethyl-dithiowrbamate Lead-diethyl-dithlooarbamate- Zinc salt of 4-hydroxyethyl-2-mercapto-thiazo- Among the acyl derivatives of dithiocarbamic acids, useful as activators for 2-mercapto-thiazolines and their salts, are- Furoyl-dimethyl-dithiocarbamate Furoyl-pentamethylene-dithiocarbamate Allyl ester of diethyl-dithiocarbamic acid Chloroacetamide ester of dicyclohexyl-dithiocarbamic acid Among the thiuram sulfides, giving good results, are- Tetramethyl-thiuram-disulfide Tetraethyl-thiuram -disu1flde Tetrapropyl-thiuram-disulfide Tetrabutyl-thiuram-disulfide Tetraamyl-thiuram-disulflde Dl-pentamethylene-thiuram-disulfide Di-hexamethylene-thiuram-disulfide Di-cyclohexyl-thiuram-disulfide Tetraethyl-thiuram-monosulfide Tetrapropyl-thiuram-monosulfide Tetrabutyl-thiuram-monosulfide Tetraamyl-thiuram-monosulfide Di-pentamethylene-thiuram-monosulfide Di-hexamethylene-thiuram-monosulfide Tetramethyl-thiuram-tetrasulfide Dihexamethylene -thiuram-tetrasulfide The combination of accelerators, employed in accordance with our invention, will generally comprise from about 1. to 100 parts of the primary accelerator for each part of the secondary Hexahydrobenzoyl-hexamethy1ene-dithiocarbamate o-Toluyl-dibutyl-dithio carbamate Alpha-naphthoyl-diethyl-dithiocarbamate Beta-naphthoyl-diamyl-dithiocarbamate Cuminyl-dibenzyl-dithiocarbamate Phthaloyl-cyclohexyl-dithiocarbamate p-Anisyl-dicyclohexyl-dithiocarbamate Butyryl-dimethyl-dithiocarbamate succinyl-methyl-ethyl-dithiocarbamate Benzoylhexamethylene-dithiocarbamate A great many difierent types of esters of dithiocarbamic acids have been disclosed as rubber accelerators. These are useful-as secondary accelerators for 2-mercapto-thiazolines or their salts, according to our invention. As examples,

the following are given:

2,4-dinitrophenyl-dimethyl-dithiocarbamate 2,4-dinitrophenyl-dibutyl-dithiocarbamate -Nitropheny1thio pentamethylene dithiocarbamate o-Nitrophenyl-thio-dicyc1ohexy1 dithiocarbamate Perchloromethyl-mercaptan ester of pentamethylene-dithiocarbamic acid Perchloromethyl-mercaptan ester of ethyl-cyclo hexyl-dithiocarbamic acid Perchloromethyl-mercaptan ester of diethyldithiocarbamic acid Dichlor-diethyl ether ester of pentamethylenedithiocarbamic acid Dichlor-diethyl ether ester of dimethyl-dithiocarbamic acid Ethyl-chloroacetate ester of alpha-methyl-pentamethylene-dithiocarbamic acid 'Ethyl-chloroacetate ester of cyclohexyl-dithiocarbamic acid Chloro-acetone ester of alpha-methyl-pentamethylene-dithiocarbamic acid Chloro-acetone ester oi furfuryl-dithiocarbamic acid accelerator. When the secondary accelerator is a carbamyl dithiocarbamate, it will generally be preferred to employ from about 1.5 to about 25 parts of the primary accelerator for each part of the carbamyl dithiocarbamate. When an ammonium salt or a metal'salt of a dithiocarbamic acid is employed as the secondary accelerator, it will generally be preferred to employ from about 2 to about parts 01 the primary accelerator to each part of the dithiocarbamic acid salt. When a thiuram sulfide is employed as a secondary accelerator, it will generally be preferred to employ from about 20 to about 50 parts of. the primary accelerator to each part of the thiuram sulfide. When an acyl derivative or ester of a dithiocarbamic acid is used as the secondary accelerator, it is preferred to employ from about 1.5 to about 25 parts of the primary accelerator for each part of the secondary accelerator.

Compounding ingredients and fillers, other than those shown in the test formulae and in other proportions, may also be used.

The combinations of accelerators herein described, namely, combinations of dithiocarbamates with 2-mercapto-thiazolines, are capable of producing highly desirable types of vulcanized rubber. These combinations produce stocks having very'high moduliand tensiles, a fast fiat cure at ordinary curing temperatures, and freedom from reversion. These qualities are not obtained at the expense of processing safety, as the stocks have little tendency to prevulcanize.or scorch. The vulcanized rubber, prepared according to our invention, also has exceedingly good resistance toward tear, abrasion, flex-cracking, and heat build-up. Another characteristic r of great value is the great resistance against deterioration by heat o'r oxidation shown by these vulcanizates. On the whole, the combination of desirable properties, produced by the mixtures of accelerators of our invention, is one that is very difllcult to duplicate with any other known accelerator or combination of accelerators, and certamly cannot be duplicated by the combination of dithiocarbamates with any types of accelerators, other than those disclosed as part of our invention.

Combinations of the amine salts, metal salts, acyl derivatives and esters with the 2-mercaptothiazolines are claimed more specifically in later to vulcanization, an accelerator of the group consisting of 2-mercapto-thiazolin'es and metal salts thereof in which the valences of the metals are dithiocarbamic acid is derived from a secondary amine, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

3. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of Z-mercapto-thiazolines and metal salts thereof in which the valences of the metals are satisfied by 2-mercapto-thiazoline radicals only, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid in which the .dithiocarbamic acid is derived from a secondary amine wherein at least one of the radicals attached to the nitrogen is an aliphatic radical, as

accelerator to each part of the secondary accelerator.

7. Rubber having incorporated therein, prior to vulcanization, 2-mercapto-thiazoline, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid, as a secondary accelerator, there being from about 1 'to about 100 parts of the primary accelerator to each part of the secondary accelerator.

8. Rubber having incorporated therein, prior to vulcanization, Z-mercapto-thiazoline, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid in which the dithiocarbamic acid is derived from a secondary amine, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator;

9. Rubber having incorporated therein, prior to vulcanization, 2-mercapto-thiazoline, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid in which the dithiocarbamic acid is derived from a secondary amine wherein at least one of the radicals attached to the nitrogen is an aliphatic radical, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

10. Rubber having incorporated .therein, prior to vulcanization, 2- -mercapto-thiazoline, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid in which the dia secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

4. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of 2-mercapto-thiazolines and metal salts thereof in which the valences of the metals are satisfied by Z-mercapto-thiazoline radicals'only, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid in whichv the dithiocarbamic acid is derived from a secondary amine wherein at least one of the radicals attached to the nitrogen is an alkyl radical, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

5. Rubber having incorporated therein, prior to vulcanization, an accelerator oi the group consisting of Z-mercapto-thiazolines and metal salts thereof in which the valences of the metals are satisfied by 2-mercapto-thiazoline radicals only, as a primary accelerator, and an accelerating derivative of a dithiocarbamic acid in which the dithiocarbamic acid is derived from a dialiphatic amine, as a secondary accelerator, there being from about 1 to about 100 parts oi the primary accelerator to each part'oi the secondary accelerator.

6. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of Z-mercapto-thiazolines and metal salts thereoi in which the valences oi! the metals are thiocarbamic acid is derived from a secondary amine wherein at least one of the radicals attached to the'nitrogen is an alkyl radical, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

11. Rubber having incorporated therein, prior to vulcanization, 2-mercapto-thiazoline, as a primary accelerator, an accelerating derivative of a dithiocarbamic acid in which the 'dithiocarbamic acid is derived from a dialkyl amine, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

12. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of z-mercapto-thiazolines and metal salts thereof in which the valences of the metals are satisfied by 2-mercapto-thiazoline radicals only, as a primary accelerator, and a thiurain sulfide, accelerator, as a secondary accelerator, there being from about 1 to about 100 parts of the primary accelerator to each part of the secondary accelerator.

i'romaboutltoaboutloopartsottheprimary'lt 13. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of z-mercapto-thiazolines and metal salts thereof in which the valences of the metal are satisfied by Z-mercapto-thiazoline radicals o y. as a primary accelerator, and a thiuram sulfide accelerator, as a secondary accelerator. there being from about 20 to about 50 parts of the primary accelerator to each part of the secondary accelerator. T

14. Rubber having incorporated therein, prior to vulcanization. an accelerator of the group consisting of z-mercapto-thiazolines and metalsalts thereof in which the valences or the metals are satisfied by -2 -mercapto-thiazoline radicals only. as a primary. accelerator, and a thiuram sulfide accelerator derived fromatecondary mine. as

a secondary accelerator, there bein from about from about 20 to about 50 parts oi the primary accelerator to each part of the secondary accelerator. r

16. Rubber.having incorporated therein, prior to vulcanization, an accelerator of the group consisting of 2-mercapto-thiazolines and metal salts thereof in which the valences of the metals are satisfied by Z-mercapto-th'iazolin radicals only, as a primary accelerator, and a tetraalkyl thiuram sulfide accelerator, as a secondary accelerator, there being from about 20 to about 50 parts of the primary accelerator to each part of the secondary accelerator.

17. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting-oi 2-mercapto-thiazolines and metal salts thereof in which the valences of the metals are satisfied by Z-mercapto-thiazoline radicals only, as a primary accelerator, and a tetramethyl thiuram sulfide accelerator, as a secondary accelerator, there being from about 20 to about 50 parts of the primary accelerator to each part of the secondary accelerator.

18. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of Z-mercapto-thiazolines and metal salts thereof in which the valences of the metals 'are satisfied by 2-mercapto-thiazoline radicals only, as a primary accelerator, and tetramethyl thiuram mcnosulfide, as a secondary accelerator, there being from about 20 to about 50 parts of the primary accelerator to each part of the secondary accelerator.

19. Rubber having incorporated therein, prior to vulcanization, an accelerator of the group consisting of 2-mercapto-thiazolinesand metal salts thereof in which the valences of the metals are satisfied by Z-mercapto-thiazoline radicals only, as a primary accelerator, and tetramethyl thiuram disulfide, as a secondary accelerator, there being from about 20 to about parts of the primary accelerator to each part of the secondary accelerator.

-20. Rubber having incorporated therein, prior to vulcanization, 2-mercapto-thiazoline, as a primary accelerator, and a thiuram sulfide accelerator, as a secondary accelerator, there being from about 20 to about 50 parts of the primary accelerator to each part ofthe secondary acce erator.

21. Rubber having incorporated therein, prl to vulcanization, Z-mercapto-thiazoline, as primary accelerator, and a t'etraalkyl thiuram sulfide accelerator, as a secondary accelerator, there being From about 20' to about 50 parts of the primary accelerator to each part of the secondary accelerator.

22. Rubber having incorporated therein, prior to vulcanization, 2-mercapto-thiazoline, as a primary accelerator, and tetramethyl thiuram monosulfide, as a secondary accelerator, there being from about 20 to about 50'parts of the primary accelerator to each part of the secondary accelerator.

-23. Rubber having incorporated therein, prior to vulcanization, 2-mercapto-thiaz'oline, as a primary accelerator, and tetramethyl thiuram disulfide, as a secondary accelerator, there being from about 20 to about 50 parts of the primary accelerator to each part of the secondary accelerator.

ARTHUR M. NEAL. BERNARD M. STURGIS.

cmnumolm: OF conmzc'r oiv. Potent 1(0. 3 5:55 4-- May 19, 19 2;

- -mm :1. REAL, ET .L

It is hereby certified that error appears in the printed specification of theabove nunbered patent requiring correction as follows: Page 6, Table II, line2of columns 2, h, 6 and 8, for "28" read --28 C.--;' same line, colmnns 5, 7 a9, for 100" read 1 oo c.'--; line 5 same table, 001- umns 2 to'9 inclusive, strike out 9 C23 and that the said Letters Patent should be read' with this-correction the-rein that the 58,1116 may conform to the record of the cm in' the Patent Office.

Signed and sealed this 28th daypf July, A. D. 1912.

Henry Van lxrs dale (Seal) Acting Commissioner of .Ifatent s. 

